OR/15/053 Dunstaffnage Castle

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Everett, P A, Gillespie, M R and Tracey, E A. 2015. Provenance of building stones in four 'galley castles' in Argyll. British Geological Survey Internal Report, OR/15/053.

Dunstaffnage Castle is located at the mouth of Loch Etive, roughly 6 km northeast of Oban. The castle was built on a peninsula that extends north-eastwards from the southern shore of the loch, providing an ideal position to command the seaward approach. To the southeast of the castle Dunstaffnage Bay provides a sheltered anchorage for ships.

Layout and building chronology

Dunstaffnage Castle is comprised of a massive 2-storey Curtain Wall with Parapet Walk, Towers at the north and west corners, and Entrance Gateway with forestair at the east corner. The Curtain Wall foundations were laid to the configuration of the underlying rock outcrop. The inner courtyard comprises of the Gatehouse, East Dwelling House, Northwest Dwelling House, and Well. A timeline of construction and alterations for Dunstaffnage Castle is presented in Table 4.

Table 4 Timeline of construction and alteration in Dunstaffnage Castle
Information from RCAHMS (1975) [1]
Date Action Location or masonry element
Mid-13th C* Construction Curtain Walls with Arrow Slits and Parapet Walk, North and West Corner Tower, Entrance Gateway, Gatehouse, East Dwelling House, Northwest Dwelling House, Well
Late-15th to Early-16th C Reconstruction Entrance Gateway
Late-16th C Reconstruction Gatehouse, upper storeys
Late-16th C Remodelled Northwest Dwelling House
Early- to Mid-17th C Remodelled Gatehouse, ground floor subdivision
Early- to Mid-17th C Reconstruction SW and SE Curtain Wall Arrow Slits (for firearm defence)
Early- to Mid-17th C Reconstruction Curtain Wall Parapets
Early- to Mid-17th C Reconstruction West Corner Tower, upper storeys
Late-17th and 18th C Minor repairs All
1725 Remodelled Northwest Dwelling House
1725 Reconstruction North end of East Curtain Wall
1725 Repairs East Range Dwelling House
1810 Gutting Gatehouse (due to fire)
Late-19th C Reconstruction Entrance Gateway Forestair
20th C Repairs All

* The original construction was thought to have been completed c.1220 by Duncan Dubhgall. His son, Ewen, may have added the three
corner towers (including the current Entrance Gateway) at a later date.

Figure 12 Plans for Dunstaffnage Castle with periods of construction and alteration. Source: RCAHMS (1975) [1]; pages 200–201, 203.

Building stones

Walling stone

The Curtain Walls are constructed of coursed random rubble blocks with a rough natural finish. Most of these are part of the original phase of construction. The walls are well-bonded with ‘pinnings’ and contain numerous larger blocks and split boulders set on edge (Figure 13a). The walling stones consist mainly of lava, granite and metasandstone; these rock types are featured in all stages of the walling, although later sections include blocks of pyrite-bearing metamudstone and Devonian sandstone. Most of these materials are probably from sources local to the castle.

Decorative stone

Assigning different stone types to the different stages of building in Dunstaffnage castle is challenging because stones from earlier parts of the castle have been re-cycled throughout its history and because there are numerous stages of building. The East Dwelling House provides a good example. The house was erected in the 13th century but is now in a ruinous state; at the north end of the dwelling the fireplace and flue were constructed from sandstone blocks recovered from Dunstaffnage Chapel. During the year 1740 sandstone dressings were re-used following the dismantling of the East window of the Chapel and the erection of the Campbell Dunstaffnage burial enclosure (RCAHMS, 1975)[1].

In the following text only examples of building elements that probably have not been affected by re-cycling are discussed.

White to buff sandstone

Uniform white to buff sandstone is the main decorative stone used in the Curtain Walls, and probably dates from the earliest, 13th century, phase of construction. This sandstone surrounds original, unmodified arrowslits on the curtain wall (Figure 13a, b), and forms a row of quoins on an angled corner of the Curtain Wall on the SW range of the castle (Figure 13c) which date from the earliest phase of construction. The same stone has been used in the nearby Chapel, which has a similar date of construction.

Thin sections were prepared from two detached fragments of sandstone, one from Dunstaffnage Castle and another from the Chapel (see Appendix 1). Microscope examination of these has shown that the same sandstone was used in the castle and the Chapel, and that the sandstone contains tiny fragments of carbonaceous matter (former plant matter) and iron oxide patches formed when an iron-rich carbonate mineral cement dissolved. These characteristics, and the presence of a much larger fragment of carbonaceous material in one of the sandstone blocks (Figure 13b), indicate that the sandstone is almost certainly of Carboniferous age.

The sandstone has characteristics that are broadly similar to those in BGS samples of Carboniferous sandstone from Inninmore Bay. This observation is consistent with a record in RCAHMS (1975)[1], which states that the stone was probably sourced from Ardtornish (near Inninmore):

“Most of the 13th century dressings are formed of a rather coarse-grained stone of iron-stained buff colour… and probably deriving from the Ardtornish area”

The following statement also appears in RCAHMS (1975)[1]:

“Here and there in the early work, however, and more extensively in the later, a finer-grained stone of greenish-yellow hue is found, and this may derive from the Carsaig beds in Mull.”

A greenish-yellow sandstone was not encountered during our site visit; however, many of the arrowslits and quoins are in inaccessible locations so the possibility that the castle contains a sandstone of this description cannot be ruled out.

Light buff sandstone

A light buff sandstone with buff to orange staining, featuring cross-bedding and carbonaceous laminae has been used to form surrounds of the point-arch recess and round-arch doorway, and quoins, of the Entrance Gatehouse. These modifications probably date from the late 15th century–16th century. Some of the original dressings here are suffering from stone decay, and some of the doorway dressing stones have been replaced in modern times (Figure 13d).

The geological characteristics of this stone suggest it is Carboniferous sandstone. This sandstone and the white to buff sandstone described in (see White to buff sandstone) are closely similar in many respects but not identical; nevertheless, the likeliest source of this sandstone is probably the Inninmore Bay/Ardtornish are of Morvern.

Flaggy purplish sandstone

Tabular blocks of flaggy purplish sandstone, almost certainly of Devonian age, have been used to form lintels and arches in 16th century alterations, notably in and near to the Northwest Dwelling House (Figure 13e). The northwest Dwelling House was remodelled in 1725; however, incorporations of 16th century fireplaces and window dressings remain. (RCAHMS, 1975[1]; page 205), suggesting the flaggy purplish sandstone may have been used in 16th and/or 18th century additions. This stone was probably sourced from a bed of sandstone in the Kerrera Sandstone Formation, which crops out close to the coast in several places between Dunstaffnage and Loch Feochan.

Light grey sandstone

Light grey, fine-grained, uniform, quartz-rich sandstone with a granular (‘sugary’) texture, has been used to form fireplaces and dressings in the Northwest Dwelling House (Figure 13f). These elements probably date from the late 16th century at the earliest, but may have been introduced in later modifications.

A sample of the stone was not collected, but its appearance is closely similar to a BGS sample of Loch Aline White Sandstone (Figure 7). The available evidence therefore suggests this stone was sourced from an outcrop near Loch Aline.

Gritty buff sandstone

Buff, gritty sandstone that typically contains fractures and mineral veins has been used extensively in the Gatehouse, for example to form the first floor window surrounds. These are thought to date from the 16th and 17th centuries, although extensive re-cycling of masonry by this time could have incorporated stone which had been used in previous structures.

The gritty buff sandstone may be Carboniferous, as its appearance is broadly similar to many Scottish Carboniferous sandstones. A sample of this sandstone type could not be collected for analysis, therefore its provenance is not constrained with greater certainty.

Uniform buff sandstone

Blocks of uniform buff sandstone have been used to form crowsteps, chimneys, and roofing tiles on the Gatehouse roof. These features date from the mid- to late- 20th century, and the sandstone was probably imported from the Midland Valley of Scotland or from England.

Pyrite-bearing metamudstone

A single, tabular slab of pyrite-bearing metamudstone has been used to form the lintel of an alcove in the Northwest Dwelling House kitchen. This stone has characteristics that are typical of roofing slates produced from the Easdale Slate Formation in the ‘slate islands’ around Easdale, and is probably originally from that area.

Figure 13 Decorative stone in Dunstaffnage Castle.
a – sandstone dressings around an arrow slit in the West Tower. b – a block of weathered sandstone with a large fragment of carbonaceous matter, in the West Tower. c – sandstone quoins on the north-east elevation of Dunstaffnage Castle. d – sandstone dressings around the inner arched doorway that now forms the main entrance (east elevation) to the Castle. e – tabular blocks of purplish Devonian sandstone and metamorphic rock used to form an arch on the SW side of the Northwest Dwelling House. f – a fireplace formed of light greenish sandstone on the northwest (back) wall of the Northwest Dwelling House; the greenish colour is probably due to biogenic growth on the surface of the stone.

References

  1. 1.0 1.1 1.2 1.3 1.4 1.5 RCAHMS. 1975. Argyll: an inventory of the ancient monuments, Vol. 2 Lorn. HMSO Press: Edinburgh